Cyclo[4]carbazole, an Iodide Anion Macrocyclic Receptor

Article abstract of DOI:10.1021/acs.orglett.6b02500

A novel preorganized and rigid iodide anion macrocyclic receptor, cyclo[4]carbazole (Cy[4]C), is reported here. The structure of Cy[4]C was confirmed by single-crystal X-ray analysis. The binding affinity of Cy[4]C for iodide anion was investigated by UV-vis and ¹H NMR spectroscopic techniques. The crystal structure of the complex between Cy[4]C and chloroform also provided evidence for the recognition ability of Cy[4]C toward iodide anion. Furthermore, the 1:1 complexation stoichiometry between Cy[4]C and iodide anion was confirmed by high-resolution mass spectrometry and molecular modeling.

Full text of DOI:10.1021/acs.orglett.6b02500

Letter
pubs.acs.org/OrgLett
Cyclo[4]carbazole, an Iodide Anion Macrocyclic Receptor
†
†
‡
†
†
†
Huangtianzhi Zhu, Bingbing Shi, Kexian Chen, Peifa Wei, Danyu Xia, Julfikar Hassan Mondal,
,†
and Feihe Huang*
†State Key Laboratory of Chemical Engineering, Center for Chemistry of High-Performance & Novel Materials, Department of
Chemistry, Zhejiang University, Hangzhou 310027, P. R. China
‡
College of Food and Biology Engineering, Zhejiang Gongshang University, Hangzhou, Zhejiang 310018, P. R. China
*
S Supporting Information
ABSTRACT: A novel preorganized and rigid iodide anion
macrocyclic receptor, cyclo[4]carbazole (Cy[4]C), is reported
here. The structure of Cy[4]C was confirmed by single-crystal
X-ray analysis. The binding affinity of Cy[4]C for iodide anion
1
was investigated by UV−vis and H NMR spectroscopic
techniques. The crystal structure of the complex between
Cy[4]C and chloroform also provided evidence for the
recognition ability of Cy[4]C toward iodide anion. Further-
more, the 1:1 complexation stoichiometry between Cy[4]C and iodide anion was confirmed by high-resolution mass
spectrometry and molecular modeling.
1
−5
18,19
nions play indispensable roles in various fields.
Specifically, iodide anion is vital for many biochemical
activities and exists in many biostructures. For example, the Na /
might show stronger binding affinity toward specific guests,
A
we rationally designed and synthesized a preorganized, rigid
macrocycle cyclo[4]carbazole (Cy[4]C) which can perform as a
new iodide anion receptor. It was made in one pot via
intermolecular coupling reaction of N-butyl-3,6-dibromocarba-
+
−
I symporter (NIS), an important plasma membrane glyco-
protein, mediates active iodide anion transport for thyroid
6
hormone biogenesis, and thyroid hormones participate in
zole using bis[1,5-cyclooctanediene]nickel(0) (Ni[COD] )
2
7
20
several metabolic processes. Hence, iodide content in foods and
(
Scheme 1). Considering that aryl C−H groups form stronger
21
drinks is often required nutritional information, and a dose of
hydrogen bonds with anions than alkyl C−H groups, it was
anticipated that this macrocycle should be able to bind anions
owing to its π-conjugated system and proper cavity size.
Interestingly, we found that Cy[4]C recognizes iodide anion in
chloroform, resulting in a distinct color change visible to the
naked eye. Our further studies ascribe this recognition to the
preorganization of the macrocycle, its suitable cavity size, and the
cooperative effect of multiple hydrogen bonds. The innovative
application of this preorganized macrocycle offers us a new way
to detect iodide anion or design new anion receptors.
8
8
0−150 μg of dietary iodine per day is recommended.
Consequently, the search for new iodide anion receptors is
9
essential in terms of nutritional studies and biological relevance.
In the past several decades, many anion receptors have been
1
0
reported, and the main factors that influence the interactions
between receptors and anions have been explored, such as
preorganization and complementary stereoelectronic arrange-
11
ment of the receptors. A substantial number of these anions
receptors are macrocycle-based. Good examples are fluorinated
macrocyclic ethers reported by Farnham that bind fluoride
Initially, in order to enhance its solubility, the NH group of 3,6-
1
2
anion, Anslyn’s bicyclic cyclophane that combines planar
dibromocarbazole was substituted by an alkyl group. Enlightened
13
oxyacid anions such as nitrate anion, a calixpyrrole reported by
20,22
by cyclization reactions using Ni[COD]2,
the synthetic
1
4
Sessler that complexes fluoride anion, and macrocycles
conditions for Cy[4]C were optimized. MALDI-TOF mass
spectrometry is a valuable tool for structure detection and
distinction. Actually, peaks of cyclo[n]carbazole (Cy[n]C) (n =
containing triazoles reported by Flood that perform as hosts
1
5
for various anions. These macrocycles commonly have
symmetric structures and preorganized binding sites that enable
strong binding affinity toward specific anionic guests. However,
most of these macrocycles are receptors for fluoride, chloride, or
4
, 5, 6, 7) macrocycles with various sizes, including an intense
peak at 885 corresponding to Cy[4]C, were found in the
MALDI-TOF spectrum (Figure S3). Moreover, this MALDI-
TOF spectrum demonstrated that N-butyl-3,6-dibromocarba-
zole preferred to form cyclic structures instead of linear
oligomers because peaks related to linear oligomers could be
1
6
oxyacid anions; few show recognition toward iodide anion.
17
Due to its large diameter and low electron density, the iodide
anion hardly forms hydrogen bonds and anion−π interactions,
resulting in the lack of recognition by conventional macrocycles.
Therefore, the discovery of new iodide anion receptors is very
important but is still a challenge for chemists.
2
3
hardly found. Pure Cy[4]C was obtained by column
Enlightened by the concept proposed by Cram and co-workers
Received: August 21, 2016
that preorganized macrocycles with preorganized binding site
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.6b02500
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
−
−
−
−
−
−
Scheme 1. Synthesis and Chemical Structure of Cy[4]C and
Cartoon Representation of Iodide Anion Recognition by
Cy[4]C
monium salts (TBAX, X = F , Cl , Br , I , AcO , H PO ,
2 4
−
−
ClO , NO ) was added into solutions of Cy[4]C in
4
3
a
chloroform to form colorless transparent mixtures, respectively.
Surprisingly, 2 h later, the solution containing Cy[4]C and TBAI
became light yellow, whereas the other solutions remained
colorless; this indicated interactions between Cy[4]C and iodide
anion. In order to investigate the recognition ability of Cy[4]C
for iodide anion, we carried out a series of host−guest
recognition experiments in chloroform. First, UV−vis experi-
ments were used to verify the binding behavior between Cy[4]C
and iodide anion (Figure 2). From the UV−vis spectra, the
a
COD: cis-1,5-cyclooctanediene.
chromatography and characterized by NMR spectroscopy
(
Figures S4 and S5).
The structure of Cy[4]C was proven by single-crystal X-ray
analysis (Figure 1). The single crystal of Cy[4]C was obtained by
−
3
Figure 2. UV−vis spectra of Cy[4]C (2.00 × 10 mM) in CHCl and
3
−
−
−
−
−
mixed solutions of Cy[4]C and TBAX (X = F , Cl , Br , I , AcO ,
−
−
−
H PO , ClO , NO ) (50.0 equiv). Inset: photograph showing the
2
4
4
3
colors of these mixed solutions.
solution of Cy[4]C (2.00 μM in CHCl ) exhibited one
3
maximum absorption band at 300 nm. Upon addition of 50.0
equiv of TBAI, the absorption band at 300 nm ascended
accompanied by a new absorption band at 360 nm, manifesting
that a new moiety formed in solution. However, the addition of
5
0.0 equiv of other TBAX mentioned above did not interfere
Figure 1. Ball-and-stick view of the X-ray crystal structure of Cy[4]C:
a) top view; (b) side view. Nitrogens are red. Hydrogens were omitted
for clarity.
with the absorption band of Cy[4]C, which indicated that
Cy[4]C could recognize iodide anion in chloroform. Subsequent
fluorescence emission spectra also demonstrated the responsive-
ness of Cy[4]C toward iodide anion. As shown in Figure S6, the
fluorescence emission intensity of Cy[4]C decreased after the
addition of TBAI to the solution of Cy[4]C.
As previously mentioned, the association process of Cy[4]C
and iodide anion is not accomplished rapidly. Time-dependent
absorption measurements for a 1:50 mixture of Cy[4]C and
TBAI in chloroform showed that the absorption band changed
gradually with time (Figure S7a). We plotted the absorbance
intensity at 360 nm versus the complexation time (Figure S7b).
According to the plot, the complexation was completed in
approximately 2 h. Therefore, the data about the investigation of
the complexation between Cy[4]C and TBAI were recorded 2 h
after TBAI addition to the solution of Cy[4]C.
(
slow evaporation of a solution of Cy[4]C in a 1:1 chloroform/n-
pentane mixture. In the top view (Figure 1a), all nitrogen atoms
are located external to the cavity, and the average distance
between nuclei of two para-positioned hydrogens, such as H and
a
H , is 6.40 Å, meaning that Cy[4]C has a cavity with a diameter
d
of 4.00 Å since the van der Waals radius of the hydrogen atom is
2
4a
1
.20 Å. This cavity diameter is smaller than the diameter of
iodide anion (4.40 Å) and larger than the diameters of fluoride
anion, chloride anion, and bromide anion (2.57, 3.62, and 3.92 Å,
2
4b
respectively). In the side view (Figure 1b), the ring is almost
planar with a small twist because of its π-conjugated system. This
crystal structure indicates that the cavity of Cy[4]C is
preorganized to bind iodide anion.
Additionally, in order to further investigate the binding
1
The crystal structure of Cy[4]C prompted us to determine
whether it is a new receptor for iodide anion. To evaluate this,
commercially available tetrabutylammonium salts (TBAX) were
taken into consideration owing to their simple composition and
good solubility in chloroform. Thus, 50 equiv of tetrabutylam-
behavior between Cy[4]C and iodide anion, H NMR
experiments were carried out to observe chemical shift changes
of aryl hydrogens on Cy[4]C (Figure S8). Upon gradual addition
of 0.1−50.0 equiv of TBAI to a solution of Cy[4]C, the peak of
H (Figure 1) shifted downfield. A possible explanation for this
a
B
DOI: 10.1021/acs.orglett.6b02500
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
phenomenon could be the formation of hydrogen bonds
between the encapsulated electron-withdrawing iodide anion
and internal hydrogen atoms of Cy[4]C. The hydrogen bonds
reduced the internal aryl electron density resulting in a downfield
solution of Cy[4]C and TBAI also indicated 1:1 complexation
stoichiometry between Cy[4]C and iodide anion (Figure S9).
An energy-minimized structure of the Cy[4]C/iodide anion
complex created via PM6 molecular modeling validated the
existence of hydrogen bonds between internal aryl hydrogens
and iodide anion. As shown in Figure 4, the iodide anion is
25
shift of the H peak. Simultaneously, the peaks related to Hb
a
and H shifted upfield, respectively, after the addition of TBAI to
c
the solution of Cy[4]C, which also confirmed the host−guest
2
6
recognition.
In order to further verify the host−guest complexation
between Cy[4]C and iodide anion, we attempted to obtain the
single crystal of the complex between Cy[4]C and I− but
unfortunately failed. However, a single crystal of a 1:1 complex of
Cy[4]C and chloroform was obtained by the solvent diffusion
method (Figure 3). In the top view (Figure 3a), one chlorine
Figure 4. Energy-minimized structure of Cy[4]C and iodide anion
complex simulated by Gaussian computer program.
Figure 3. Ball-and-stick views of the crystal structure of the Cy[4]C/
chloroform complex: (a) top view; (b) side view. Hydrogens are blue,
nitrogens are red, and chlorines are green. Hydrogens except those
involved in interactions between Cy[4]C and chloroform were omitted
for clarity. H···Cl distances (Å) and C−H···Cl angles (deg) of hydrogen
located at the center of macrocycle (for the top view, see Figure
4
; for the side view, see Figure S10). The average distance
between the iodide anion and each surrounding hydrogen is 3.07
Å, smaller than the sum, 3.40 Å, of the van der Waals radii of the
hydrogen atom and the iodide anion, indicating the possible
existence of hydrogen bonds between all eight internal aryl
hydrogens and the iodide anion. The results of molecular
24
.
..
bonds: A, 3.15, 170; B, 3.23, 167. Cl···C distances (Å) of C−Cl π
interactions: C, 3.75; D, 4.06.
1
modeling are consistent with the aforementioned H NMR
atom is located at the center of Cy[4]C, and two distances (A
and B in Figure 3) between the chlorine atom and two internal
aryl hydrogen atoms on the ring are marked. The interactions
between the chlorine atom and these two hydrogen atoms can be
considered as hydrogen bonds according to a previously reported
criterion, 2.000 Å < d(H···Cl) < 3.300 Å and C−H···Cl angle
spectra (Figure S8), for which the peak related to internal
hydrogens in NMR shifts downfield due to the hydrogen bond
formation. Besides, compared with the encapsulated chlorine
atom, the larger iodide anion has a just suitable size to match and
fill the whole cavity of Cy[4]C, resulting in the binding of
Cy[4]C to iodide anion.
2
7
>
90°. The distances between the chlorine atom and the other
To further study the binding affinity of Cy[4]C toward iodide
six internal aryl hydrogen atoms vary from 3.325 to 3.375 Å, and
anion, UV−vis absorption spectral variation of Cy[4]C (4.00 ×
28
−3
their interactions can be regarded as van der Waals interactions.
10 mM) in CHCl was monitored during titration with
3
Hydrogen bonds and van der Waals interactions are the main
forces to fix the chlorine atom at the center of Cy[4]C. The other
two chlorine atoms of the chloroform molecule form C−Cl···π
interactions (C and D in Figure 3) with Cy[4]C. This also
helps to stabilize the Cy[4]C/chloroform complex. In the side
view (Figure 3b), the Cy[4]C macrocycle in the complex is
obviously twisted compared with the structure of Cy[4]C alone
different concentrations of TBAI from 0.0 to 5.00 equiv. We
found that with an increasing amount of TBAI the absorption
intensity at 360 nm gradually increased (Figure S11). The
29
−1
association constant (K ) was determined to be 81.8 ± 9.2 M
a
for 1:1 complexation by a plot of absorption intensity alternation
versus TBAI concentration. Considering Cy[4]C is an electron-
30
rich macrocycle, this association constant is reasonable.
(
Figure 1). This twisted conformation is conducive to the
In summary, we synthesized a preorganized, rigid macrocycle,
cyclo[4]carbazole, and its structure and host−guest interactions
toward halide anions were studied. Cyclo[4]carbazole shows
colorimetric and fluorencent recognition for iodide anion in
chloroform. The crystal structure of the Cy[4]C/chloroform
complex as well as HRMS implied its ability to encapsulate iodide
anion to form a 1:1 complex. Moreover, the planar structure of
Cy[4]C with an inner cavity diameter of 4.00 Å provides an ideal
size for iodide anion complexation. The energy-minimized
structure study shows that iodide anion matches the cavity of
Cy[4]C exactly and forms multiple hydrogen bonds with the
host. As a new receptor for iodide anion, Cy[4]C has potential to
formation of hydrogen bonds and can provide a suitable binding
geometry for chloroform. These results indicate that the long
complexation complete time of iodide anion by Cy[4]C is
possibly because of the competitive complexation of iodide anion
and chloroform toward Cy[4]C. In addition, the preorganization
19
compensates the lower intrinsic affinity of aryl C−H donor,
and hence, this π-conjugated, rigid macrocycle has the ability to
form hydrogen bonds and complex with a halide anion guest.
The Cy[4]C/chloroform complex crystal structure implies that
the binding ratio between Cy[4]C and halide anion is 1:1.
Actually, the high-resolution mass spectrum (HRMS) of a
C
DOI: 10.1021/acs.orglett.6b02500
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
play an important role in iodide anion sensing and provide a new
perspective to design iodide anion receptors.
(9) Kumari, N.; Hasan, M. A.; Ward, B. D.; Mishra, L. Ind. Eng. Chem.
Res. 2013, 52, 15007−15014.
(
10) (a) Cai, J.; Sessler, J. L. Chem. Soc. Rev. 2014, 43, 6198−6213.
(b) Busschaert, N.; Caltagirone, C.; Van Rossom, W.; Gale, P. A. Chem.
ASSOCIATED CONTENT
Supporting Information
■
Rev. 2015, 115, 8038−8155. (c) Bull, S. D.; Davidson, M. G.; Van Den
Elsen, J. M. H.; Fossey, J. S.; Jenkins, A. T. A.; Jiang, Y.-B.; Kubo, Y.;
Marken, F.; Sakurai, K.; Zhao, J.; James, T. D. Acc. Chem. Res. 2013, 46,
312−326. (d) Li, A.-F.; Wang, J.-H.; Wang, F.; Jiang, Y.-B. Chem. Soc.
Rev. 2010, 39, 3729−3745. (e) Edwards, S. J.; Valkenier, H.; Busschaert,
N.; Gale, P. A.; Davis, A. P. Angew. Chem., Int. Ed. 2015, 54, 4592−4596.
*
S
Experimental details, NMR spectra, UV−vis spectra, X-ray
crystallographic files (CIF) for Cy[4]C and its chloroform
complex and other materials. These materials are available free of
charge via the Internet at The Supporting Information is available
free of charge on the ACS Publications website at DOI: 10.1021/
acs.orglett.6b02500.
(f) Zhang, R.; Zhao, Y.; Wang, J.; Ji, L.; Yang, X.-J.; Wu, B. Cryst. Growth
Des. 2014, 14, 544−551. (g) Langton, M. J.; Serpell, C. J.; Beer, P. D.
Angew. Chem., Int. Ed. 2016, 55, 1974−1987. (h) Barendt, T. A.;
Robinson, S. W.; Beer, P. D. Chem. Sci. 2016, 7, 5171−5180.
(11) Horng, Y.-C.; Huang, P.-S.; Hsieh, C.-C.; Kuo, C.-H.; Kuo, T.-S.
Chem. Commun. 2012, 48, 8844−8846.
Experimental details, NMR spectra, UV−vis spectra, X-ray
crystallographic data for Cy[4]C and its chloroform
complex and other materials (PDF)
X-ray data for Cy[4]C (CIF)
X-ray data for Cy[4]C and chloroform (CIF)
(
12) Farnham, W. B.; Roe, D. C.; Dixon, D. A.; Calabrese, J. C.;
Harlow, R. L. J. Am. Chem. Soc. 1990, 112, 7707−7718.
13) Bisson, A. P.; Lynch, V. M.; Monahan, M.-K. C.; Anslyn, E. V.
(
Angew. Chem., Int. Ed. Engl. 1997, 36, 2340−2342.
AUTHOR INFORMATION
Corresponding Author
■
*
(14) Kim, S. K.; Lynch, V. M.; Young, N. J.; Hay, B. P.; Lee, C.-H.; Kim,
J. S.; Moyer, B. A.; Sessler, J. L. J. Am. Chem. Soc. 2012, 134, 20837−
2
0843.
E-mail: fhuang@zju.edu.cn.
Notes
(
15) Hua, Y.; Flood, A. H. Chem. Soc. Rev. 2010, 39, 1262−1271.
(16) (a) Li, Y.; Pink, M.; Karty, J. A.; Flood, A. H. J. Am. Chem. Soc.
2
008, 130, 17293−17295. (b) Yawer, M. A.; Havel, V.; Sindelar, V.
The authors declare no competing financial interest.
Angew. Chem., Int. Ed. 2015, 54, 276−279. (c) Singh, N.; Jang, D. O. Org.
Lett. 2007, 9, 1991−1994. (d) Mendy, J. S.; Saeed, M. A.; Fronczek, F.
R.; Powell, D. R.; Hossain, M. A. Inorg. Chem. 2010, 49, 7223−7225.
ACKNOWLEDGMENTS
■
This work was supported by the National Basic Research
Program (2013CB834502), the National Natural Science
Foundation of China (21434005, 91527301, J1210042), the
Fundamental Research Funds for the Central Universities, the
Key Science Technology Innovation Team of Zhejiang Province
(
17) Lee, D. Y.; Singh, N.; Kim, M. J.; Jang, D. O. Org. Lett. 2011, 13,
024−3027.
18) Cram, D. J. Angew. Chem., Int. Ed. Engl. 1988, 27, 1009−1020.
(19) Ilioudis, C. A.; Tocher, D. A.; Steed, J. W. J. Am. Chem. Soc. 2004,
3
(
126, 12395−12402.
(
2013TD02), and the Open Project of State Key Laboratory of
(20) Coumont, L. S.; Veinot, J. G. C. Tetrahedron Lett. 2015, 56, 5595−
5
598.
Supramolecular Structure and Materials (sklssm201611).
(
21) Bryantsev, V. S.; Hay, B. P. J. Am. Chem. Soc. 2005, 127, 8282−
283.
22) Nakanishi, W.; Yoshioka, T.; Taka, H.; Xue, J. Y.; Kita, H.; Isobe,
H. Angew. Chem., Int. Ed. 2011, 50, 5323−5326.
23) Ostrauskaite, J.; Strohriegl, P. Macromol. Chem. Phys. 2003, 204,
713−1718.
24) (a) Bondi, A. J. Phys. Chem. 1964, 68, 441−451. (b) Shannon, R.
D. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr.
976, A32, 751−767.
25) (a) Duan, Q.; Xia, W.; Lin, C.; Pan, Y.; Wang, L. Tetrahedron Lett.
015, 56, 4002−4006. (b) Yu, G.; Zhang, Z.; Han, C.; Xue, M.; Zhou,
8
(
REFERENCES
■
(
1) (a) Jones, J. W.; Zakharov, L. N.; Rheingold, A. L.; Gibson, H. W. J.
Am. Chem. Soc. 2002, 124, 13378−13379. (b) Safarowsky, C.; Merz, L.;
Rang, A.; Broekmann, P.; Hermann, B. A.; Schalley, C. A. Angew. Chem.,
Int. Ed. 2004, 43, 1291−1294. (c) James, S. J.; Perrin, A.; Jones, C. D.;
Yufit, D. S.; Steed, J. W. Chem. Commun. 2014, 50, 12851−12854.
d) Zhu, K.; Zhang, M.; Wang, F.; Li, N.; Li, S.; Huang, F. New J. Chem.
008, 32, 1827−1830. (e) Zhu, K.; Li, S.; Wang, F.; Huang, F. J. Org.
(
1
(
(
2
1
(
2
Chem. 2009, 74, 1322−1328. (f) Zhu, K.; Wu, L.; Yan, X.; Zheng, B.;
Zhang, M.; Huang, F. Chem. - Eur. J. 2010, 16, 6088−6098. (g) Gibson,
H. W.; Jones, J. W.; Zakharov, L. N.; Rheingold, A. L.; Slebodnick, C.
Chem. - Eur. J. 2011, 17, 3192−3206.
Q.; Huang, F. Chem. Commun. 2012, 48, 2958−2960.
(
(
26) Lee, S.; Chen, C.-H.; Flood, A. H. Nat. Chem. 2013, 5, 704−710.
27) Allen, F. H.; Kennard, O. Chem. Des. Autom. News. 1993, 8, 31−
(
2) (a) Foster, J. A.; Edkins, R. M.; Cameron, G. J.; Colgin, N.; Fucke,
3
7.
K.; Ridgeway, S.; Crawford, A. G.; Marder, T. B.; Beeby, A.; Cobb, S. L.;
Steed, J. W. Chem. - Eur. J. 2014, 20, 279−291. (b) Sun, S.; Hu, X.-Y.;
Chen, D.; Shi, J.; Dong, Y.; Lin, C.; Pan, Y.; Wang, L. Polym. Chem. 2013,
(
28) Thallapally, P. K.; Nangia, A. CrystEngComm 2001, 3, 114−119.
29) Nayak, S. K.; Reddy, M. K.; Guru Row, T. N.; Chopra, D. Cryst.
Growth Des. 2011, 11, 1578−1596.
30) Wang, D.-X.; Zheng, Q.-Y.; Wang, Q.-Q.; Wang, M.-X. Angew.
Chem., Int. Ed. 2008, 47, 7485−7488.
(
4
, 2224−2229. (c) Ji, X.; Yao, Y.; Li, J.; Yan, X.; Huang, F. J. Am. Chem.
Soc. 2013, 135, 74−77.
3) (a) Zhao, J.; Yang, D.; Zhao, Y.; Yang, X.-J.; Wang, Y.-Y.; Wu, B.
(
(
Angew. Chem., Int. Ed. 2014, 53, 6632−6636. (b) Kumar, R.; Srivastava,
A. Chem. - Eur. J. 2016, 22, 3224−3229.
(
4) Davis, C. M.; Ohkubo, K.; Lammer, A. D.; Kim, D. S.; Kawashima,
Y.; Sessler, J. L.; Fukuzumi, S. Chem. Commun. 2015, 51, 9789−9792.
(
5) Ko, S.-K.; Kim, S. K.; Share, A.; Lynch, V. M.; Park, J.; Namkung,
W.; Van Rossom, W.; Busschaert, N.; Gale, P. A.; Sessler, J. L.; Shin, I.
Nat. Chem. 2014, 6, 885−892.
(
6) Dai, G.; Levy, O.; Carrasco, N. Nature 1996, 379, 458−460.
(
7) Taurog, A. The Thyroid: A Fundamental and Clinical Text;
Lippincott Williams & Wilkins: Philadelphia, 2000; pp 61−85.
8) (a) Zimmermann, M. B. Semin. Cell Dev. Biol. 2011, 22, 645−652.
b) Zimmermann, M. B.; Jooste, P. L.; Pandav, C. S. Lancet 2008, 372,
251−1262.
(
(
1
D
DOI: 10.1021/acs.orglett.6b02500
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